how to make them last. - weat - north texas section | north … · · 2017-07-20to avoid...
TRANSCRIPT
7/20/2017
1
How they work,
How they fail,
How to make them last.
CENTRIFUGAL PUMPS
BY: L. Granger Smith, P.E. ‐ Smith Pump CompanyDr. David Pierce, P.E. – Specific Energy
FOR: W.E.A.T. – North Texas SectionON: Wednesday, July 19, 2017
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
INTRODUCTION
WEAT
Optimal pump station management requires correct selection, application, and operation of pumps and motors.
The theory is straightforward and tools exist to help engineers, managers, and operators implement the theory.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
INTRODUCTION – Smith Pump Co., Inc.
WEAT
LOCATIONS
Fort Worth
Waco
Austin
Houston
EXCELLENCE
since
1962
Vital Statistics About 70 employees
Headquarters – Waco
Manufacturing – Waco
Warehouse – all four locations
Shop Services – all four locations
Motor Repair/Rewind – Fort Worth shop
Field Services – all four locations
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
INTRODUCTION – Specific Energy
WEAT
• Est. 2010 in Georgetown, Texas• Principals are from Steger & Bizzell Engineering, est. 1972
• Offerings:• Pump station monitoring
• Pump station optimization
• Lift station control
• And, of course, IIOT
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
AGENDA
WEAT
• Introduction• Pump and motor basics• Pump hydraulics• Pump station operation• Pump lifecycle management• Efficient operation• Hydraulic transients• Closing
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
OBJECTIVES (learning)
WEAT
• Proper selection and application of centrifugal pumps
• Proper selection and application of electric motors
• Factors that affect the life of a pumping unit
• Efficient operation of pump stations
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP AND MOTOR BASICS
WEAT
• Types of pumps
• Types of motors
• Electric motor characteristics
• Select a motor size
• Motor starting characteristics.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP AND MOTOR BASICS
WEAT
VERTICAL TURBINE PUMP
SUBMERSIBLE TURBINE PUMP
DIFFUSER PUMPS
The bowl assembly
• Types of pumpsCLEAR LIQUID PUMPS
VOLUTE PUMPS
Between bearing
Overhung
Horizontal split‐case
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP AND MOTOR BASICS
WEAT
VERTICAL TURBINE SOLIDS HANDLING PUMP
DIFFUSER PUMP
• Types of pumpsSOLIDS HANDLING PUMPS
For lift stations, these pumps must pass a 2.5” sphere
Dry pit solids handling
Submersible solids handling
Self priming solids handling
VOLUTE PUMPS
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP AND MOTOR BASICS
WEAT
• Types of pumpsHOW THEY WORK
WEAR RINGAREA, ONE PER SUCTION
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP AND MOTOR BASICS
WEAT
• Types of motors
OPEN DRIP PROOF
HORIZONTAL GENERAL DUTY
TEFC HORIZONTAL SEVERE DUTY
WP-IVERTICALHOLLOW
SHAFT HIGH
THRUST
VSS TEAAC HIGH THRUST
VSS TEWAC NORMAL THRUST INDUCTION
EXPLOSION PROOF HORIZONTAL
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP AND MOTOR BASICS
WEAT
• Electric motor characteristics Performance
Motors are generally more efficient at 75% load than at 100% load.
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP AND MOTOR BASICS
WEAT
• Electric motor characteristics Performance
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP AND MOTOR BASICS
WEAT
• Electric motor characteristics Performance Selection
RATED C.O.S.Q = 14,757 gpmH = 140 ftE = 86.0%P = 607 hp
ACTUAL C.O.S. FLOWQ = 15,200 gpmH = 140 ftE = 91.0%P = 591 hp
TOLERANCE C.O.S. FLOWQ = 16,000 gpmH = 140 ftE = 86.0%P = 658 hp
700 hp
Sometimes the peak horsepower doesn’t occur at the C.O.S.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP AND MOTOR BASICS
WEAT
• Electric motor characteristics Performance Selection Motor starting characteristics
Motor Torque• 100% voltage• 90% voltage• 60% voltage
Pump Torque• Open valve• Closed valve
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head• Series & parallel operation• Field‐measured curves
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static headDISCHARGE
PUMP
h = h
static suctionh
SUCTION
total statich
h-
static dischargeh
total static static discharge static suction
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head
StaticDischargeHead
Static Suction HeadDatum
Total Head = Static Suction Head+Static Discharge Head
Static
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head
System curves are made up of
two fundamentalcomponents ‐ the static
head and the frictional head
120
80
40
0
Hea
d, ft
500040003000200010000Flow rate, gpm
Static Head
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head• Friction head
friction
atm
atmos. press.
ASSUME
static suction
total friction
static suction
total static
total headhh
h
PUMP
static discharge
total static ==
hh
hh
+-
frictionh
SUCTION
p
h
atmos. press.
total statichp
DISCHARGE
p
h
atm= p
static discharge
Besides static head we also
have to consider friction and atmospheric
head
• Static head• Friction Head
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Friction Head– HAZEN AND WILLIAMS formula for water
hf = 0.002083 L (100/C)1.85 x gpm1.85 / d4.8655
where: hf = friction head (ft)L = length of pipe (ft)C = Hazen Williams friction factor (60 to 160)
gpm = flow of liquid (gal/min)d = inside diameter of circular pipe (in)
HAZEN AND WILLIAMS formula for waterC = Hazen Williams friction factor (60 to 160)
For “STEEL” pipe the head can vary as follows…EXAMPLES: NEW DESIGN BASIS OLDC Factor 150 130 100 80Multiplier 0.47 0.62 1.00 1.50
Since old pipe friction can be 3 times new
pipe, we must consider both new and old.
• Static head• Friction head• Total Dynamic Head
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
+ FRICTION LOSSES
+ GAUGE ELEVATIONDISCHARGE HEAD
+ VELOCITY HEAD
TOTAL HEADDYNAMIC
• Static head• Friction Head
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
System curves are made up of
two fundamentalcomponents ‐ the static
head and the frictional head
120
80
40
0
Hea
d, ft
500040003000200010000Flow rate, gpm
Total
Static Head
Friction
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head• Friction head• Total dynamic head• Pump performance curves
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
WEAT
FLOW
BEP
BEP
HEAD VS CAPACITY
BEP = Best Efficiency Point
TYPICAL PUMP PERFORMANCE CURVE
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves
TYPICAL PUMP PERFORMANCE
CURVE
Max Impeller
Min Impeller
Rated Impeller
C.O.S.
C.O.S. = Condition Of Service
Brake Horsepower
R.P.M.
C.O.S.
MODEL
M.C.S.F.
NPSHr
A.O.R.P.O.R.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head
NPSHr
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head
Net Positive Suction Head (available)
NPSH
NPSHa = hs + hatm– hvp
To Avoid CavitationNPSHAvailable>NPSHRequired
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head
To Avoid CavitationNPSHAvailable>NPSHRequired
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head
To Avoid CavitationNPSHAvailable>NPSHRequired
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head• Series & parallel operation
The Vertical Turbine Pump can be a pump in series.
PUMP
SUCTION PUMP
TWO
SERIESIN
PUMPS
DISCHARGE
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICSWEAT
• Static head• Friction head• Total dynamic head• Pump performance curves• Reading pump curves• Net positive suction head• Series & parallel operation
DISCHARGE
SUCTION PUMP
PUMPS
PARALLEL
TWO
IN
PUMP
SYSTEM HEAD
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS – field‐measured curves
WEAT
Severely Worn Factory Condition
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS – field‐measured curves
WEAT
• Vary the flow (full speed)• Manual
• Adjust with valve
• Vary the speed• Automatic
• Adjust with VFD
• Use affinity laws to estimate full‐speed curves
Per Pump Station:• Suction Pressure or source level• Discharge pressure• Total flow
Per pump:• Power• Speed
LT
OR
PT PT
FT
LT Level Transmitter
Pressure Transmitter
Flow Meter
PT
FT
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS – field‐measured curves
WEAT
EXAMPLE ‐ Fixed‐speed pump:
Discharge valve varied manually, data collected automatically
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS – field‐measured curves
WEAT
EXAMPLE ‐ Variable‐speed pump:
Speed varied automatically, data collected automatically
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
Field‐measured curves ‐ challenges
WEAT
• Power monitoring• Dedicated power meters
• Power from VFDs
• Estimate shaft power
• Flow monitoring• Flow meters notoriously noisy
• Prefer one meter per station
• Data collection• Manual
• Automatic
Per Pump Station:• Suction Pressure or source level• Discharge pressure• Total flow
Per pump:• Power• Speed
LT
OR
PT PT
FT
LT Level Transmitter
Pressure Transmitter
Flow Meter
PT
FT
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION OPERATION
WEAT
• Operating range• System curves and operating points• Multiple‐pump parallel operation• Variable speed and system curves• Modeling and design• DEMONSTRATION
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION OPERATION
WEAT
• Operating rangeP.O.R. – PREFERRED OPERATING RANGE(generally defined by Hydraulic Institute Standards)
Volute Pumps (aka Centrifugal)70 % QBEP 120 %
Diffuser Pumps (aka Turbine)NS 4500 70 % QBEP 120 %NS 4500 80 % QBEP 115 %
• A.O.R. – ALLOWABLE OPERATING RANGE(defined by Pump Manufacturer)
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION OPERATION
WEAT
• Operating range• System curves and operating points
FLOW
H vs QSYSTEM HEAD
The intersection determines the operating flow of the pump.
PUMP OPERATION
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
Pumps in parallel
DISCHARGE
SUCTION PUMP
PUMPS
PARALLEL
TWO
IN
PUMP
SYSTEM HEAD
FLOW
3 PUMPS2 PUMPS1 PUMP
• Operating range• System curves and operating points• Multiple‐pump parallel operation
• Operating range• System curves and operating points• Multiple‐pump parallel operation• Variable speed and system curves
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP HYDRAULICS
WEAT
200
150
100
50
0
Hea
d, ft
500040003000200010000Flow rate, gpm
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WEATCENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
• Operating range• System curves and operating points• Multiple‐pump parallel operation• Variable speed and system curves
PUMP STATION OPERATIONThis pump curve has it all.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION DESIGN
WEAT
• Step 1: Determine operating range• Range of flows• Corresponding ranges of pressures
• Step 2: Choose number and type of pumps
• Type
• Make & model
• Impeller diameter
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION DESIGN – pump selection
WEAT
• Method 1: Identify peak flow and head• Choose pumps to match
• Method 2: Identify second operating point.• Match both operating points
• Method 3: Characterize full range of operating points
• Match all operating points with pump PORs
• Method 4: Model system and demands
• Choose pumps to minimize annual cost
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION DESIGN – system definition
WEAT
Many tools exist (including Excel) to compute a range of system curves.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION DESIGN – system definition
WEAT
The range of system curves for the example system.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION DESIGN – system definition
WEAT
0
50
100
150
200
250
0 1000 2000 3000 4000 5000 6000
Flow (GPM)
Pump Head (feet)
Empirical operational data characterize desired operating range
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION DESIGN – match pumps to system
WEAT
Overlay system curves with pump preferred operating regionsto validate pump selection.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION DESIGN – match pumps to systemWEAT
Detailed model:
• Validate specific operating points
• Limit speeds to stay in POR
• Estimate behavior with worn pumps.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION DESIGN – match pumps to systemWEAT
4 pumps selected for BEP at peak flow
Limit 1 pump to 54% to stay in POR
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP STATION DESIGN – optimal pump selection
WEAT
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP LIFECYCLE MANAGEMENT
WEAT
• Lifetime pump and motor costs• Pump and motor failures• What makes pumps last• Financial basis for pump repair• DEMO: pumps needing repair
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
PUMP LIFECYCLE MANAGEMENT – lifetime costs
WEAT
Typical Pump Station: 3 x 200‐hp (room for future 4th pump)
• Capital cost: $ 2M• Capital cost, 3 pumps/motors: $ 200k• Yearly energy cost ($0.10/kWh): $ 100k• PV of energy cost (12 yrs, 3%): $ 1M• PV of 1% savings: $ 10k
• Motor efficiencies: Efficient: 95.0% Premium efficient: 96.2%• Pump efficiencies: 85% to 90%
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
Pump failures• Seals, bearings, wear rings• Corrosion, de‐alloying• Cavitation erosion• Metal fatigueMotor failures• Seals, bearings• Burnt‐out windings• Loss of insulation
THIS DAMAGE STARTED ON THE
BACK SIDE OF THE VANE.
SUCTION RECIRCULATION
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
Pump failures• Seals, bearings, wear rings
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
Pump failures• Seals, bearings, wear rings
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
Pump failures• Seals, bearings, wear rings• Corrosion, de‐alloying• Cavitation erosion• Metal fatigueMotor failures• Seals, bearings• Burnt‐out windings• Loss of insulation
10C temperaturedifference doublesInsulation life
• Bearings• Contamination• Stress & Load• Vibration• Heat• Lubrication
• Windings• Heat• Inverters• Voltage problems• Load• Contamination
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
What fails on a Motor?
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
What fails on a Motor?
VFD Spike to windings
Can see 2000V +peaks
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
What fails on a Motor?
Good coupling alignment is key to a long run between
failures.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
Extending pump and motor life – DESIGN
• Adequate NPSH• Design for operation in POR• Design for operation within recommended speeds• Materials selection• Motors on VFDs: mitigate harmonics• HVAC
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
Extending pump and motor life – INSTALLATION
• Alignment• Grouting• Identify resonant frequencies
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
Extending pump and motor life – OPERATION
• Operate pumps within POR, near BEP• Operate pumps with adequate NPSH• Operate within speed limits• Avoid resonant frequencies• Limit stops and starts
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failuresWEAT
Extending pump and motor life – DEMO
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failuresWEAT
Extending pump and motor life – DEMO
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failuresWEAT
Extending pump and motor life – DEMO
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
Extending pump and motor life – MONITORING
• Pump tests: head curve, power curve, pump health index• Vibration monitoring• Temperature monitoring• Seal‐fail detection
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MANAGEMENT – pump & motor failures
WEAT
Good Criteria For Long Pump Runs• Good pump design.• Good foundation and anchoring.• Good piping design.• Good installation.• Good operation.• Operation within the Preferred Operating Range.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MGMT – financial basis for pump repair
WEAT
• Test pumps periodically head, efficiency curves
• Estimate 12‐month energy consumption with current pumps
• Estimate 12‐month energy consumption with repaired pumps
• Compute net present value (NPV) for repairs:
Present value of reduced energy
̶ Cost of repair ̶ ̶ ̶ ̶ ̶ ̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶ ̶ ̶̶ ̶̶ ̶̶ ̶̶
NPV
• Replace / repair pump(s) when NPV > 0
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MGMT – financial basis for pump repair
WEAT
Regional Raw Water Pump Station (rural utility in SE Texas)
Per year: 4B gallons, 6200 MW‐h
Power(hp)
Pump Health Index
700 102%
700 94%
700 94%
700 92%
700 90%
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
LIFECYCLE MGMT – financial basis for pump repair
WEAT CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION
WEAT
• Pump efficiency• Other losses (VFD, motor, friction)• Specific energy: cost per MG• Specific energy vs flow• Required instrumentation• DEMO: optimal pump operation
Remember those wear rings?• Good pump design.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION – pump efficiency
WEAT
WEAR RINGAREA, ONE PER SUCTION
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION – other Losses
WEAT
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Pump Station EnergyConsumption
VFD Losses
Motor Losses
Pump Losses
Friction Losses
Useful Work
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION – minimize specific energy
WEAT
SpecificEnergy
⁄
Energy In (kWh) Work Out (MG)
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION – the operator’s problem
WEAT
32 combinations2 x 2 x 2 x 2 x 2 =
28 million combinations
31 x 31 x x x >
ON / OFF Control
VFD Speed Control
(0.5 Hz res.)
31 31 31
45 60 45 60 45 60 45 60 45 60
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION – specific energy vs flow
WEAT
Flow (gpm)
Lower Pumping CostS
peci
fic E
nerg
y (k
Wh/
MG
)
Green: All pumps in POR (1%)Orange: One or more pumps outside POR (99%)
There are 28 million ways to run the pump station.Only one optimally satisfies current demand.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION – specific energy vs flow
WEAT
Flow (gpm)
Lower Pumping CostS
peci
fic E
nerg
y (k
Wh/
MG
)
There are 28 million ways to run the pump station.Only one optimally satisfies current demand.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION – specific energy vs flow
WEAT
Flow (gpm)
Lower Pumping CostS
peci
fic E
nerg
y (k
Wh/
MG
)
There are 28 million ways to run the pump station.Only one optimally satisfies current demand.
For example, to achieve 3500 gpm, run Pump 1 at 58.4 Hzand Pump 5 at 55.8 Hz.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION – required Instrumentation
WEAT
Per Pump Station:• Suction Pressure or source level• Discharge pressure• Total flow
Per pump:• Power• Speed
LT
OR
PT PT
FT
LT Level Transmitter
Pressure Transmitter
Flow Meter
PT
FT
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
EFFICIENT OPERATION – demonstrationWEAT CENTRIFUGAL PUMPS
How they work. How they fail. How to make them last.
HYDRAULIC TRANSIENTS
WEAT
• Change in flow change in pressure• Limit transients with pump control valves• Limit transients with VFDs• Other ways to limit transients• DEMO: real pump station
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
HYDRAULIC TRANSIENTS – the theory
WEAT
Joukowsky (water hammer) equation:
∆ ∆
Where:∆ changeinhead ft∆ changeinvelocity ft/s
wavespeed ft/sgravitationalacc. 32ft/s2
Wave speed: 1200 to 3800 ft/s depending on pipe material.
5 ft/s velocity; ductile iron pipe, sudden loss of power.∆ 5ft/s
3800ft/s
∆ 5 ·380032.2
ft
∆ 590ft 256psi
PVC pipe: 1200ft/s; ∆ 186ft 81psi
Without mitigation, pressure zero, creating vapor pocket.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
HYDRAULIC TRANSIENTS – example
WEAT
Transient reduced by reflections if:
shut downperiod pipelengthwavespeed
Use PCV or VFD to limit transients.
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
HYDRAULIC TRANSIENTS – importance of pipe length
WEAT CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
HYDRAULIC TRANSIENTS – pump control valves
WEAT
Traditional solution: PCV limits ∆ during starts, stops.
Issues:• Flow through PCV is nonlinear• Delay often too short to be effective• PCVs are high‐maintenance
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
HYDRAULIC TRANSIENTS – variable frequency drives
WEAT
Simple solution: long ramp rates (acc., dec. settings)
Problems: flow is nonlinear; delay often still too short
Better solution:
• Monitor pressure• Limit flow change based on pressure
(until mitigated by reflections)
CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
HYDRAULIC TRANSIENTS – worst case: power loss
WEAT
Solutions for power loss (PCVs and VFDs ineffective):
• Surge pressure tank• Pressure relief valve• Air‐release / vacuum‐breaker valves
Pressure‐based VFD control still neededfor normal operations.
DEMONSTRATION: VFD w. & w/o control; PRV
7/20/2017
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CENTRIFUGAL PUMPSHow they work. How they fail. How to make them last.
CLOSING
WEAT
Optimal pump station management requires correct selection, application, and operation of pumps and motors.
The theory is straightforward and tools exist to help engineers, managers, and operators implement the theory.
Thank you!